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804 results on '"Im, Hyunsik"'

4. Resonantly pumped bright-triplet exciton lasing in caesium lead bromide perovskites

Author

Ying, Guanhua, Farrow, Tristan, Jana, Atanu, Shao, Hanbo, Im, Hyunsik, Osokin, Vitaly, Baek, Seung Bin, Alanazi, Mutibah, Karmakar, Sanjit, Mukherjee, Manas, Park, Youngsin, and Taylor, Robert A.

Subjects
Physics - Optics, Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science, Quantum Physics
Abstract

The surprising recent observation of highly emissive triplet-states in lead halide perovskites accounts for their orders-of-magnitude brighter optical signals and high quantum efficiencies compared to other semiconductors. This makes them attractive for future optoelectronic applications, especially in bright low-threshold nano-lasers. Whilst non-resonantly pumped lasing from all-inorganic lead-halide perovskites is now well-established as an attractive pathway to scalable low-power laser sources for nano-optoelectronics, here we showcase a resonant optical pumping scheme on a fast triplet-state in CsPbBr3 nanocrystals. The scheme allows us to realize a polarized triplet-laser source that dramatically enhances the coherent signal by one order of magnitude whilst suppressing non-coherent contributions. The result is a source with highly attractive technological characteristics including a bright and polarized signal, and a high stimulated-to-spontaneous emission signal contrast that can be filtered to enhance spectral purity. The emission is generated by pumping selectively on a weakly-confined excitonic state with a Bohr radius ~10 nm in the nanocrystals. The exciton fine-structure is revealed by the energy-splitting resulting from confinement in nanocrystals with tetragonal symmetry. We use a linear polarizer to resolve two-fold non-degenerate sub-levels in the triplet exciton and use photoluminescence excitation spectroscopy to determine the energy of the state before pumping it resonantly., Comment: 19 pages, 9 figures

Published
2021

37. Highly Efficient CoFeP Nanoparticle Catalysts for Superior Oxygen Evolution Reaction Performance.

Author

Meena, Abhishek, Ahmed, Abu Talha Aqueel, Singh, Aditya Narayan, Sree, Vijaya Gopalan, Im, Hyunsik, and Cho, Sangeun

Subjects
OXYGEN evolution reactions, METAL catalysts, CLEAN energy, SUSTAINABILITY, COMPOSITE structures
Abstract

Developing effective and long-lasting electrocatalysts for oxygen evolution reaction (OER) is critical for increasing sustainable hydrogen production. This paper describes the production and characterization of CoFeP nanoparticles (CFP NPs) as high-performance electrocatalysts for OER. The CFP NPs were produced using a simple hydrothermal technique followed by phosphorization, yielding an amorphous/crystalline composite structure with improved electrochemical characteristics. Our results reveal that CFP NPs have a surprisingly low overpotential of 284 mV at a current density of 100 mA cm−2, greatly exceeding the precursor CoFe oxide/hydroxide (CFO NPs) and the commercial RuO2 catalyst. Furthermore, CFP NPs demonstrate exceptional stability, retaining a constant performance after 70 h of continuous operation. Post-OER characterization analysis revealed transformations in the catalyst, including the formation of cobalt–iron oxides/oxyhydroxides. Despite these changes, CFP NPs showed superior long-term stability compared to native metal oxides/oxyhydroxides, likely due to enhanced surface roughness and increased active sites. This study proposes a viable strategy for designing low-cost, non-precious metal-based OER catalysts, which will help advance sustainable energy technology. [ABSTRACT FROM AUTHOR]

Published
2024
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48. Electrical Modulation of Superconducting Critical Temperature in Liquid-Gated Thin Niobium Films

Author

Choi, Jiman, R., Pradheesh, Kim, Hyungsang, Im, Hyunsik, Chong, Yonuk, and Chae, Dong-Hun

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

We demonstrate that the superconducting critical temperature (Tc) of thin niobium films can be electrically modulated in a liquid-gated geometry device. Tc can be suppressed and enhanced by applying positive and negative gate voltage, respectively, in a reversible manner within a range of about 0.1 K. At a fixed temperature below Tc, we observed that the superconducting critical current can be modulated by gate voltage. This result suggests a possibility of an electrically-controlled switching device operating at or above liquid helium temperature, where superconductivity can be turned on or off solely by the applied gate voltage., Comment: 7 pages, 5 figures

Published
2014
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